An exploration of some early transition metal (oxy) fluoride systems using solvothermal
techniques has been carried out. 30 novel materials have been synthesised, which fall into
three classes based on different metal centres; vanadium (21), molybdenum (5) and
niobium (4). Some of these also contain secondary metal centres, namely copper (22) and
zinc (1). Simultaneously, the relationship between the SHG values and the crystal
structures of the hilgardites family members Pb₂B₅O₉Cl, Pb₂B₅O₉Br, Sr₂B₅O₉Cl and
Ba₂B₅O₉Cl was investigated. In particular, the Pb–containing members of the hilgardite
family of borate halides exhibit an abnormally large non–linear optical response, which
was analysed based on neutron powder diffraction.
Using solvothermal synthesis in HF–containing media, 21 novel vanadium oxyfluorides
containing interesting structural features, were synthesised at 160˚C using a range of
organo-amine compounds as a ligand, template, linker or structure directing agent. The
architectures of the crystal structures may be categorised into; four clusters including
monomeric vanadium units, five clusters including vanadium dimers, eight 1–D chains,
two 2–D layers and two 3–D networks. ‘Composition–space’ diagrams with three
components were used to study the effect of stoichiometry changes of reactants and to
map out the crystallisation fields.
The combination of early (Nb⁵⁺, Mo⁶⁺) and late (Cu²⁺) transition metals with different
organo-amines produced nine novel compounds incorporating monomers, chains and 2–
D interpenetrated networks. The chains and layers were synthesised from a systematic
series of reactions at 160˚C and can be subdivided into four pairs, the topologies of which
are essentially unique to each ligand, containing in each case a Cu–based cationic
species, but alternately either [MoO₂F₄]²⁻ or [NbOF₅]²⁻, in an isomorphous manner, as
the anionic moiety. The overall structures of these materials reflect the influence of the
organo–amine ligands.
The materials have been studied for their magnetic properties and characterised by
thermogravimetric analysis, Rietveld refinement and elemental analysis where relevant.